1. Field of the invention.
The field of the invention relates to header assemblies for spraying press rolls during the manufacture of sheet metal.
2. Brief description of the prior art.
The cold rolling of sheet stock is accomplished by passing metal strip through at least one press nip defined by a pair of rolls. The strip is subjected to varying degrees of reduction at right angles to the direction of rolling. If excess work is performed at the center of the stock, the center elongates longitudinally more than the edges and may buckle in the center. If excess work is performed at the edges, the converse is true.
Many factors, such as quality of input stock, localized heating of the mill roll faces, or deflection of the rolls, influence these cold work variations. Since the strip is reduced not only by roll compression but also by the high tensile loads applied with the coiler, these defective areas are difficult to detect until the coil is complete. The defects that are detected during rolling are compensated for through manual adjustment of the rolling mill or through the application of coolant to the roll faces. It is important that these defects be substantially reduced, if not eliminated entirely because those areas of the sheet stock outside the acceptable flatness limits must be scrapped with resulting economic loss.
Shape sensing rolls have been developed to monitor the rolling mill output. One method of adjusting the mill to level out the force differentials has been to control the temperature of the rolls by the selective spraying of coolant. This is used in combination with a technique known as roll bending in order to arrive at the desired sheet profile.
Signals from a shape sensing roll cause the automatic adjustment of each coolant spray section to reduce uneven temperature distribution. The relative positions of the rolls may also be adjusted.
State of the art roll coolant distribution headers incorporate a series of equally spaced, electrically operated valves which are arranged so as to be able to distribute the roll coolant evenly over the faces of the rolls. The valves are designed to permit variation from uniformity of the coolant distribution on the roll faces by remote manual or automatic means. The coolant can therefore be applied so as to permit thermal crowning of the rolls toward the end goal of producing a transversely flat strip.
Roll coolant valves have traditionally been of two types. The first type includes proportional valves in which the coolant flow through the valve is approximately proportional to the voltage applied thereto. Some of these are without feedback loops and therefore are not reliably accurate. Others are equipped with feedback loops and are much more accurate, but this improvement in accuracy of flow control is accompanied by an increase in valve size, sensitivity to damage, and cost of manufacture.
A second type of roll coolant valve which has been successfully empolyed is the binary valve which comprises two or more individual on-off valves. Flow control is accomplished by having the valves sized to pass coolant at rates which are different by successive multiples of two (2). That is, 1 gpm, 2 gpm, 4 gpm, 8 gpm, etc. For example, if only two (2) valves are used, the coolant flow can be adjusted in increments of one-third of the maximum flow. That is, proper energization of the valves can provide one (1) unit of flow, two (2) units of flow, or three (3) units of flow. If three individual valves are used, the coolant can be adjusted in increments of one-seventh of the maximum flow. If four (4) individual valves are used, the increment is one-fifteenth of the maximum flow, etc. The binary valves sacrifice infinitely variable flow control for simplicty and reliability of operation with no appreciable loss in control of the transverse flatness of the strip.
State of the art flow header designs incorporate binary type valve systems. The individual valves have been integrated into one single unit which installs directly into the coolant plenum chamber. Single-stage solenoid-operated valves are utilized. The plenum chamber is fitted with pipe connections for the coolant supply lines. The spray nozzles which are supplied by the individual valves are gang-mounted in a retainer plate fastened to the plenum chamber by means of screws.
Divadvantages of the above-described system include:
1. Electrical control wiring to the individual valves must pass through areas which are completely enveloped by roll coolant. In the event of sealing device failure, coolant leakage can short the control wiring to ground causing loss of operation and/or electrical failures;
2. The single-stage valves require a relatively large electrical current to remain open against the valve spring closing force. This current requires relatively large wires and generates heat in the solenoid necessitating the solenoid being immersed in the coolant of the plenum chamber. This current also requires a relatively large power supply/controller;
3. Maintenance of any individual valve requires the removal of the entire gang of nozzles;
4. Maintenance of any individual nozzle requires the removal of an entire gang of nozzles and the complete binary valve;
5. Maintenance of the entire header, or the plenum alone, requires the removal of the feed pipes from the plenum.